A priority objective of the National Cancer Program is the requirement for biochemical and/or immunological methods for early detection of cancer based on analysis of exfoliated cells or body fluids obtained from apparently normal individuals. This invention pertains to a biochemical method of cancer detection based on serum analysis of glycolipids.
Buck et al., Science 172, 169 (1971) first reported that tumor-characteristic sialofucosyl glycopeptides, present only in trace amounts in normal cells, are considerably elevated in tumor cells. Subsequently, glycopeptide alterations have been demonstrated in tumor cells obtained from peripheral blood of patients with active leukemia by VanBeek et al., Nature 253, 457 (1975). Sialic acid-containing glycosphingolipids termed gangliosides, are also altered in the direction of increased amounts of sialic acid as reviewed by Richardson et al., Biochem. Biophys. Acta 417, 55 (1975). These studies, however, were restricted to the tumor tissues themselves, and except for detection of leukemic cells, have had little or no diagnostic applications.
More recent studies from our laboratory at Purdue University (Merritt et al., manuscript to be published in J. Natl. Cancer Inst.) show that both gangliosides and ganglioside biosynthetic enzymes are elevated in tissues surrounding tumors as well as in the tumors themselves. These studies subsequently led to a study to determine if glycolipids were also elevated in the sera of animal models. In mice bearing transplantable mammary carcinomas, serum levels of sialic acid-containing glycolipids were found to be elevated 1.5 to 3 fold on pooled serum samples from which gangliosides were purified by column chromotography by Kloppel et al., Proc. Nat. Acad. Sci. U.S.A., (to be published). An elevated and altered ganglioside pattern for pooled serum samples of Morris hepatoma-bearing rats published by Skipski et al., Biochem. Biophys. Res. Commun., 67, 1122 (1975) showed an altered pattern in serum corresponding to that of the tumor tissue. These studies, however, employed standard methods of ganglioside extraction, purification, and quantification on pooled serum samples. The methods are tedious, time consuming, and not well adapted to routine clinical usage.
If sialic acid levels are to have diagnostic implications, it is essential that serum from individuals be analyzed. To accomplish the latter, a simplified extraction and purification procedure was employed that permitted analyses of 0.5 to 1.0 ml serum.